It sounds like, since you are on a much older version of the PGP Desktop software, and you cannot find the key on the server. That you might have an expired key on your keyring as well? The email address being invalid shouldn't matter. But how are you searching for the key on PGP Universal Server? I would recommend searching by the keyid (which is also globally unique on your server) and see if you can find it there under Managed Keys.
Also make sure that you a local copy of your Organization Key in your local keyring of the PGP Client as that is used to validate your private key in your keyring.
Do you have a key, with the keyid that the PGP disk is prompting for in your keyring with the keypair (icon of both keys) in your keyring under "my private keys"?